Almost all present day stern drives are of the type having a solid, generally upright drive column through which the power is transmitted by shaft and bevel gear means. Thus, such conventional stern drives have a substantial width of shaft housing in front of the prop, causing turbulence and loss of prop efficiency.
A generally horizontally arranged cavitation plate disposed just above the prop is an essential element of any modern high-performance stern drive, and in the conventional shaft and bevel gear type stern drive such cavitation plate normally extends from proximate the leading edge of the solid drive column along the sides thereof and extending rearwardly over the prop. A further problem in such conventional stern drives is that the body of water that sweeps up behind the boat when it is moving rapidly requires the provision of a second, upper horizontal plate that is spaced above the cavitation plate and which serves as a deflector to hold down the up-swept water. This second plate causes much of the up-swept water to be diverted laterally behind the solid drive column, creating substantial additional drag.
Another problem in conventional stern drives is that the substantial width required for the solid drive column precludes any thin fin-like configuration thereof within allowable front-rear length limitations for truly clean hydrodynamic passage through the water, or for effective functioning thereof as a rudder or keel means.
A still further problem in connection with conventional stern drives is the use of separate hydraulic trim and tilt mechanisms which have exposed hoses. Hydraulic feedback generally causes the trim to be altered by changes in boat speed, RPM and the like, requiring the operator to be continually readjusting the trim. The conventional swing-up release associated with such mechanisms is a one-way hydraulic valve means that normally will not trim back to the same setting.
A variety of belt-driven stern drives have been proposed for many years, but none of these have been truly successful or competitive with other types of boat drives. A principal reason for the failure of most prior art belt-driven sterm drives is that the construction thereof precluded clean hydrodynamic lines, so that they generally produced excessive drag in the water. In particular, the construction of such prior art belt-driven marine drives was generally such as to produce substantial turbulence in the water flow to the prop if the drive components were forward of the prop, causing poor prop efficiency and likelihood of prop burn. This in some instances caused the makers of such prior art belt drives to place the prop forward of the drive components, which is not presently acceptable because of the likelihood of prop damage from underwater obstructions.
A further problem in connection with prior art belt drive attempts of this type was that there was no satisfactory means disclosed in the art for introducing high tension forces into the belt, whereby the employment of a very wide, thin, steel cable reinforced belt of the type capable of transmitting large amounts of power under high belt tensioning was precluded.
A further problem in connection with prior art belt-driven stern drives was that they had no satisfactory means for providing access to the belt such that the belt could be readily inserted into and removed from the drive; and in particular there was no means disclosed in such prior art which would enable a continuous power drive belt of the wide, thin, cable-wound type required for large power transmitting to be inserted and removed as a continuous, unseparable loop.